Distillation of tar



Feb. 4, 1936. A. A. M CUBBIN ET AL 2,029,883

DI STILLATION OF TAR Filed Aug. 14, 1930 2 Sheets-Sheet 1 fondenser fonlanser (l/amber Vapor flan er W3 INVENTORS fl. Ii. MacCubb/n 1/. f avert ik d:

ATTORNE 6'6: fer

m swag 960/015 Feb. 4, 1 936. A. A. MMCUBBIN ET AL 3 DISTILLATION OFITAR Filed Aug. 14, 1930 2 Sheets-Sheet2 Vac uum (SW/l INVENTORS 11/7. MacCubb/n v.24, Iii/w: 1%

ATTOR I Patented Feb. 4, 1936 UNITED STATES PATENT oFFicE 2,029,883 DISTILLATION 0F TAR Application August 14, 1930, Serial No. 475,194

13 Claims.

This invention relates to an improved method of distilling tar and obtaining a high yield of distillate therefrom, or distillate of improved grade or both. The invention includes both the method and apparatus for carrying it out. The word tar" is intended to include cqal tar (such as coke oven, gas house, low temperature tars, etc.), water gas tar and the like.

The invention relates to a multi-stage distilling operation, one stage of which is carried out under a high vacuum. The material in the vacuum still is heated during the distillation therein, according to the preferred form of the invention, by indirect contact with heated coal tar which is itself being subjected to the treatment of the improved process. The temperature of this heated tar is reduced by heat interchange with the material in the vacuum still and it is then reheated and distilled, preferably in a pipe coil still, and the residue from this distillation is subjected to further distillation in the vacuum still. The distillate from each of the stages of the distillation process is collected separately.

The first stage of the distillation, exclusive of a preliminary topping operation, is advantageously carried out in a pipe coil still. The vacuum distillation which follows makes use of the heat contained in the high temperature residue from the first distillation and additional heat is supplied by indirect contact with untreated coal tar heated in a pipe coil. This material is then reheated in another pipe coil and flashed in the vapor box of the pipe coil still. The vacuum distillation is preferably accomplished without heating the residue from this vapor box to a higher temperature than the material is heated in the pipe coil of the pipe coil still.

.In the operation of pipe coil stills generally for the distillation of tar the residue produced as a result of the distillation is usually drawn off at a high temperature as a finished product and is employed as fuel, or it may be permitted to cool and solidify with a semi-solid or solid consistency,

or it may be passed to other stills in which it is subjected to further distillation for the production of additional oil and a harder or higher melting point residue or coke therefrom. When pipe coil stills are employed for simple distillatio'n, there is a limit to the extent to whichthe distillation can be carried because if the tar is heated to too high temperatures some of it is decomposed, with the result that there is an increase in the free carbon content of the pitch produced, a' reduction in oil yield, and the production of oils of lower grade. If the raw material is kept at a sui ficiently low temperature to avoid decomposition, the oil yields are limited and the extent to which the distillation may be carried is also limited.

The present invention enables high oil yields to be obtained and high-grade residual products are produced in a continuous manner and with the avoidance of objectionable overheating of the coal tar material being distilled, and it enables the pipe coilstill to be operated at a temperature such that decomposition is avoided or minimized.

According to the present invention, the coal tar or a topped or partially distilled product, is subjected to heating by pumping it continuously through a pipe coil in a pipe coil still. This heated material is then passed in indirect heat interchanging relation with the material being distilled in the vacuum still.. The undistilled tar is then reheated in a pipe coil of the pipe coil still and discharged therefrom into a vapor chamber where the vapors are separated from the unvaporized residue. The unvaporized residue is then withdrawn to the vacuum still where it is subjected to a high vacuum, and heat is supplied thereto from the heated untreated coal tar by indirect contact therewith, and further oils are distilled therefrom and a high melting point pitch or viscous residue is produced together'with an additional amount of distillate of high boiling range.

Where desirable, a multi-stage pipe coil still with a plurality of vapor boxes may be employed for'the preliminary distillation of the coal tar before it is subjected to the high vacuum distillation, and one or more of the vapor boxes may be operated under a partial vacuum.

In the present process the high vacuum is not applied directly to the vapor chamber of the pipe coil still but is applied to the hot residue produced by the pipe coil still distillation after the residue has been withdrawn from the vapor chamber of this still. The vapors separated in the vapor chamber of the pipe coil still may advantageously be passed to a condenser without being subjected to a vacuum. The application of a vacuum to the vapor chamber of the pipe coil still would add to the difficulty of condensing the distillate owing to the necessity of operating the condenser at .lower temperatures to secure effective condensation of the lighter oils, and the expansion of the large amount of light oil vapors, etc. In the preferred form of the present process, the vacuum is applied only to the residue from the pipe coil still after it has been freed from vapors in the vapor chamber so that the h vacuum causes the distillation of heavy oil contained in the residue which heavy oil vapors can be readily condensed by cooling in a high vacuum. It is, however, within the scope of the invention to apply it'to the residue of a distillation carried out under diminished pressure where such a series of steps is desirable.

In carrying out the present process it is advantageous to use the untreated tar first as a condensing medium for the vapor produced by the distillation, thereby preheating it at the same time that the distillation vapors are cooled. This preheating is accomplished in the condensers and heat interchanger through which the vaporized' material is pumped under pressure and in indirect heat interchanging relation with the vapors. By regulation of the process the material can be preheated in this way to a temperature sufllcient to distill off some of the lighter oils by discharging the preheated material into a vapor box or chamber where the light vapors are separated and from which they are withdrawn to a condenser. The light oils, for example, benzol, toluol, xylol, naphthalene, phenols, etc., may be distilled from the tar by such preheating.

The coal tar thus preheated and freed from part of its lower boiling oils is then heated in a pipe coil and used for heating the residue from the pipe coil distillation while it is subjected to distillation under a high vacuum. It is then reheated in a pipe coil still under. some pressure and to a high temperature, and discharged into a vapor box or chamber where the oil vapors are separated from the residual unvaporized material. The preheating of the tar to be used for heating in the vacuum still is preferably so regulated that at no time is the material heated to a higher temperature than the temperature to which it is heated in the pipe coil just prior to flashing in the vapor box. In this way undue thermal decomposition of the tar is avoided. When, however, it is desired to introduce a-maximum amount of heat into the vacuum still, the tar may be heated to a higher temperature. for this purpose than it is subsequently subjected to.

.The residue from the vapor chamber of the pipe coil still is passed continuously to a vacuum box or still where it undergoes further distillation and where an additional amount of heavy oil is distilled therefrom and a heavier residue produced. This vacuum distillation is advantageously a film distillation in which a thin film of the residue 'from the pipe coil distillation is caused to flow in indirect contact with the preheated coal tar while the pipe coil distillation residue is being subjected to a high vacuum.' In

the vacuum still, the vacuum maintained is preferably 27 to.29.7 inches of mercury, for example,

' vantage that the tar can be rapidly and continuously distilled by continuously pumping it through the pipe coil at a high velocity and heating it therein to a high temperature without maintaining it at a high temperature for more than a very short period of. time, thus minimizing danger of decomposition of the oil. The coal tar heated to a high temperature in the pipe coil still is immediately discharged into the vaporchamber of the still where it is somewhat cooled by the vaporization which takesplace. The vapors are drawn oil and separately condensed. The residue from the vapor chamber is at a high temperature, and it is subjected to further distillation under high vacuum with the addition thereto of heat by indirect contact with the untreated tar heated in the pipe coil and which is to be reheated and then flashed into the vapor chamber. The maximum temperature to which the material is heated is preferably attained in the pipe coil immediately prior to flashing in the The improved apparatus of the present invention includes a pipe coil still and a vacuum still so connected that the hot residue from the pipe coil still and an associated vapor box passes directly to the vacuum still, and the vacuum still is provided with a heating chamber which is connected with the coil of the pipe coil still for re- ,heating the hydrocarbon material discharged,

from the heating chamber. The apparatus also includes a pipe coil heater for heating the un treated tar material prior to entering the heating chamber of the vacuum still. The apparatus also includes condensers and heat interchangers in which the tar can be preheated and from which the preheated material may be discharged into a vapor box or'separating chamber for separation of vapors of low boiling oils therefrom. The resulting topped tar flows to the pipe coil heater. It is advantageous to employ a pipe coil heater which comprises the coil for heating the hot tar supplied to the heating chamber of the vacuum still, and also the coil or coils of a single stage or multi-stage pipe coil still which are connected with one or more vapor chambers.

The coal tar is heated to a high temperature under some degree of pressure and discharged from the single stage or multi-stage pipe coil still into the one or more vapor boxes or separating chambers where the vapors are separated from the undistilled residue. The vacuum box or still ed while the residue is being heated by indirect contact with the hot tar which is continuously circulated through the heating chamber.

The residue from the vacuum still may be further treated for the production of coke, etc., and where such further treatment is contemplated, the apparatus includes an additional still or stills or suitable apparatus for such further treatment.

The process and apparatus of the present invention enable a wide range of oil fractions to be produced and enable the diiferent fractionations to be regulated to obtain fractions suitable for various purposes without further fractionation. The process can be operated, for example, to produce from coal tar various products such as light oil; and one or more tar acid oil fractions; creosote oil and resinous oil fractions can also be obtained.

The'temperature to which the coal tar is'heated in the pipe coil still can be varied but in general the temperature should not be sumciently high to cause objectionable decomposition of the material passing through the still. However, by pumping the material through the still at a rapid rate it can be momentarily heated to high temperature immediately prior to its discharge from the heating coil without any appreciable decom-- position taking place. The primary heating of the material in the pipe coil prior to use in the heating chamber of the vacuum still is preferably so regulated that the material ls not heated therein to a temperature higher than the temperature to which it is heated in the pipe coil still prior to flashing in the'vapor chamber. The temperature to which the material can be heated without appreciable decompositon will vary, but the process and apparatus can be so operated that the residue produced in and withdrawn from the vapor chamber of the still may have a temperature approaching the decomposition temperature. In the treatment, a temperature somewhat lower than 700-800 F. will ordinarily be employed.

The invention will be further described in connection with the accompanying drawings, which are of a conventional or diagrammatic character but it is intended and is to be understood that the invention is not limited thereto:

Fig. 1 is in the nature of a flow sheet and shows arrangements and apparatus embodying the invention and adapted for the practice of the process thereof;

Fig. 2 is a detail showing the heating chamber of the vacuum still;

Fig. 3 shows a modified form of heating chamber; and

Fig. 4 is a horizontal section on line 44 of Fig. 3.

In Fig. 1 a storage tank I for the crude or raw.

coal tar is shown. A pump 2 is provided for bringing the material into indirect contact with the vapors in the fractionating condenser 3. The partially preheated material passes through the line 4 into the fractionating condenser 5 and from there through the line 6 into the fractionating condenser I. It then passes through the line 8 into the vapor chamber 9 where lower boiling oils are volatilized and separated from the residue. The vapors pass to the condenser 3 and the residue may be drawn oil to the storage tank Ill -or pumped directly-by the pump ll into the pipe coil l2 in the heater l3.

The vacuum still I4 is provided with a heating chamber I5 which is shown somewhat in detail in Fig. 2. The coal tar heated in the pipe coil l2 enters the heating chamber through the line l6 and passes around the tubes ll of the heating chamber where it comes into indirect contact with the material being subjected to vacuum distillation inthe vacuum still l4, and supplies hea thereto. It is returned through the line l8 to the pipe coil heater where it is reheated in the pipe coil l9, and then passes through the line 20 to the vapor chamber 2 I. In the vapor chamber oil vapors are separated from the distillation residue. The vapors pass to the condenser I where they are condensed and one or more oil fractions are produced.

The residue from the vapor chamber is drawn off through the line 22 and passes through the regulation valve 23 into the vacuum still I l. The vacuum chamber is ordinarily placed at a higher level-than the vapor chamber and may be positioned above the vapor chamber and the reduced pressure in the vacuum still draws the residue from the vapor chamber up through the line 22 into the vacuum still. The residue from the distillation in the vapor chamber is still hot when it'enters the vacuum still. It is sprayed into the vacuum still or otherwise more or less evenly distributed over the heater therein and the residue is further distilled because of the low pressure in the still and because of the heat supplied from the hot tar in the heating chamber 15. Additional distillate including vapors of higher boiling oils is produced.

A three-stage vacuum pump of the ejector type is shown at 24. Any type of vacuum pump suitable for maintaining a high vacuum of preferably 27 or more inches of mercury may be employed. This vacuum pump is connected with the vacuum still through the condenser 5 where one or more oil fractions may be condensed.

The residue from the vacuum distillation is .drawn off through the pipe 28 to the storage tanks 25. Oil receivers are shown at 26 sufficient in number to collect the oil fractions produced. Heat interchangers 21 are shown for recovering heat from the condensate and supplying it to the material to be distilled. Where a high boiling condensate which is solid or semi-solid at ordinary temperatures is produced in the condenser 5, the receivers 26 connected with this condenser will be placed closely adjacent thereto and insulation or steam jackets will be provided to prevent hardening of the condensate in the pipes connecting the condenser with the receivers. The residue from the vacuum distillation may beutilized as desired.

In the distillation of coke oven tar, for example, the storage tank I may contain raw tar. This tar is first employed as a cooling medium in the con-- densers. the vapors from the vapor chamber 9 in the condenser 3 and is heated to a temperature of F., or higher, for example. It is then used as the cooling medium in the condenser 5 for condensing vapors from the vacuum still. The vapors from the vacuum still are largely condensed at this temperature even though under high vacuum. The tar then flows in indirect contact with the vapors in the condenser I and is flashed in the vapor chamber 9. The final sections of each of the condensers are advantageously cooled with water as indicated.

In the vapor chamber 9 moisture and lighter oils such as benzol and toluol, etc., are vaporized and after being condensed in the condenser 3 this light oil is collected in one or more oil receivers 26. The tar is then heated in the pipe coil l2 and after passing through the heating chamber of the vacuum still it is reheated in the coil l9 and flashed in the vapor chamber 2|. Here tar acid oils, and, by proper regulation, light creosote oils, are also produced. These are condensed and as many fractions as desired are produced and separately collected in the oil receivers 26. This distillation is ordinarily carried out at or about atmospheric pressure except where a multi-stage pipe coil still is employed and then two or more vapor chambers are provided and one or more of thesemay then be maintained under a partial vacuum to advantage.

The residue from this distillation is drawn by vacuum through the line 22 into the vacuum still l4 where it is subjected to a high vacuum, for example 27 to 29.7 inches or more. The distillate which is condensed in the condenser 5 comprises higher boiling creosote oils and high boiling viscous or resinous constituents which are semi-solid or solid at ordinary temperatures in an isolated It first flows in indirect contact with v of that still.

state. These compounds may be collected in one or two or more oil receivers 26.

The residue from this vacuum distillation is a high melting point pitch with a melting point which may 'be in the neighborhood of 400 F.,-

or higher. It may advantageously be coked or it may be otherwise treated as desired. An oil yield of or or more may be obtained, depending upon the type of tar distilled. Lower melting point pitches may also be produced, with correspondingly lower oil yields by operating at lower temperatures. Relatively improved oil yields are obtained also under these conditions as compared with oil yields obtained by the usual pipe coil still distillation to pitches of like melting points. Various modifications of the apparatus here disclosed may be employed within the scope of the invention. The condenser 3, for example, may

be replaced or supplemented by a scrubber with wash oil to recover light oil vapors from the distillation of tar, etc. Other types of vacuum pump and various types of condensers, dephlegmating towers, .etc., may be employed.

In Figs. 3 and 4 a modified type of vacuum still and heating chamber is shown. In this arrange ment the heating medium enters through the pipe l6 and flows through the tubes 31 and back to be reheated in the pipe coil still and" the material being distilled fiows down over the tubes 31 in the form of a film and is subjected to distillation under the vacuum maintained in the vacuum still and is simultaneously heated by the hot tar flowing through the tubes 31. The residue from the distillation is drawn off through the pipe 28' to storage.

It will be seen that the present process and apparatus provide for applying a high vacuum in the vacuum still to the residue produced by a prior distillation, preferably without applying the vacuum to the vapor separating chamber of the prior distillation still, and during the high vac-. uum distillation, the material being distilled is heated to a temperature which is preferably less than the temperature to which the tar is heated in the pipe coil prior to flashing in the vapor box In the preferred embodiment of our invention, the vapors are taken off from the primary distillation at substantially atmospheric pressure, though at times the vapors may be under a pressure slightly over atmospheric pressure, and in some instances a partial vacuum. which will usually not exceed a few inches of mercury may be employed. Only the residue from theprior distillation is drawn oil and subjected to a high vacuum. The heavy distillate produced under the high vacuum can be readily condensed even at the high vacuum because of the absence of lower boiling constituents. The high vacuum can be much more readily maintained where only the hot residue is thus subjected to the vacuum than where the vacuum is applied directly to the entire vapor of the pipe coil still in the vapor box Moreover, the cond nsation of the heavy distillate from the separat d residue can be more readily accomplished under a high vacuum than the condensation of the entire vapor production of the pipe il still. A high vacuum can be readily maintaQi by a suitable vacuum Dump.

It will thus be seen that the present invention provides an improved method and apparatus for distilling coal tar in a continuous manner and with notable heat economy as well as with vthe production of a high-grade pitch and a high oil yield. It will be further seen that the distillation is accomplished without overheating of the material being distilled and that the maximum temperature to which it is subjected in the pipe coil still prior to flashing in the vapor box is not exceeded in the further distillation of the residue therefrom.

. The invention is also applicable to the treatment of tar distillate oils. In the appended claims, the term hydrocarbon material" is intended to includev tar distillate oils.

We claim:

1. The method of treating tar which comprises distilling the tar, separating the vapors and liquid residue produced thereby, heating the residue by indirect heat transfer from heated tar passing to the first mentioned distillation stage and subjecting the said residue to a second distillation efiected at a lower pressure.

2. The method of treating tar which comprises distilling the tar, separating the vapors and liquid residue produced thereby, subjecting the residue to a second distillation effected under a lower pressure while supplying heat thereto by indirect heat transfer from heated tar passing to the first rial which comprises distilling the material, separating the vapors and liquid residue produced thereby, heating the residue by indirect heat transfer from heated hydrocarbon material passing to thefirst mentioned distillation stage, and subjecting the said residue to a second distillation efiected under a vacuum.

5. The method of distilling hydrocarbon materialin a plurality of stages including distillation under difi'erent pressures, which comprises heating the hydrocarbon material, passing the heated material through the heating chamber of a low pressure still in indirect heat interchanging relation with material being distilled therein, re-

heating the hydrocarbon material and subjecting it to partial distillation in a still operating at a higher pressure, and subjecting the residue from this distillation to distillation in the low pressure still while supplying heat thereto from the heated hydrocarbon material passing through the'heating chamber.

6. The method of distilling hydrocarbon material in a plurality of stages including distillation under a vacuum which comprises heating the material, passing the material through the heating chamber of a vacuum still in indirect heat interchange relation with the material being distilled therein, reheating the material and subjecting it to partial distillation, and subjecting the residue from this distillation to distillation in the vacuum still while supplying heat thereto from the heated material passing through the heating chamber.

7. The method of distilling hydrocarbon material in a pluralityof stages which comprises heating the hydrocarbon material, passing it through the heating chamber of a vacuum still in indirect contact with the material being subjected to distillation therein, subjecting the material as it flows from the heating chamber to distillation by heating to a temperature sufficient to vaporize a considerable proportione of the oil contained therein and then discharging the material into a vapor separating chamber, drawing off the resulting vapors and subjecting the residue to distillation under a vacuum in the vacuum still while simultaneously supplying heat thereto from the hot hydrocarbon material in the heating chamber of the vacuum still.

8. The method of distilling tar to pitch of a high melting point in a plurality of stages which comprises heating the tar to a temperature not greater than that to which the tar is heated in a subsequent heating step, passing the heated tar through the heating chamber of a vacuum still in indirect heat interchanging relation with tar being distilled in the'vacuum still, reheating. the tar after it leaves the heating chamber, then from the flashing operation to further distillation under a vacuum while supplying heat thereto from the heated tar passing through the heatin chamber of the vacuum still.

9. Apparatus for distilling hydrocarbon material comprising a primary still, a second still including means for maintaining the same under an operating pressure lower than that of the primary still, a heating chamber in the second still for bringing a heating medium into indirect contact with the material being distilled therein, means for heating hydrocarbon material, means for circulating hydrocarbon material through the heating means, thence to the heating chamber in the second still, and then to the primary still for distillation therein, and means for conducting residue from the primary still to the vacuum still.

10. An apparatus for distilling hydrocarbon material comprising a pipe coil heater, a preliminary distillation still, and a vacuum still, a vacuum pump for maintaining a vacuum on the vacuum still, and a heating chamber in the vacuum still for bringing a heating medium into indirect contact with the material being distilled therein, separate condensers connected with the pipe coil still and the vacuum still, and means for passing hydrocarbon material continuously through the pipe coil heater into the heating chamber of the vacuum still, thence through the preliminary distillation still and into a vapor chamber connected to such still, and means, including pressure-regulating means, for conducting the residue from the distillation in the vapor chamber into the vacuum still. i

11. Apparatus for distilling liquid material in a multi-stage distillation operation comprising a still, a second still, means for transferring liquid residue from the first still to the second still, means for operating the second still at pressure lower than the first still, a heater, a heating chamber in the second still for bringing heating medium into indirect contact with material being distilled in said second still, means for passing liquid material through the heater and the heating chamber in the second still, and means for passing the liquid material into the first still.

12. The method of distilling hydrocarbon material which comprises distilling the material, separating thevapors and liquid residue produced thereby, heating theresidue by indirect heat transfer from heated hydrocarbon material passing to the first mentioned distillation stage, and

operating at a higher pressure than the first mentioned stage.

ALEXANDER A. MACCUBBIN.

JOSEPH ZAVER'I'NIK, JR. 

